package com.jn.langx.util.reflect.type;


import com.jn.langx.util.Preconditions;
import com.jn.langx.util.collection.ConcurrentReferenceHashMap;

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;


/**
 * Helper class for resolving generic types against type variables.
 *
 * <p>Mainly intended for usage within the framework, resolving method
 * parameter types even when they are declared generically.
 *
 */
public abstract class GenericTypeResolver {

    /** Cache from Class to TypeVariable Map */
    @SuppressWarnings("rawtypes")
    private static final Map<Class<?>, Map<TypeVariable, Type>> typeVariableCache =
            new ConcurrentReferenceHashMap<Class<?>, Map<TypeVariable, Type>>();


    /**
     * Determine the target type for the given parameter specification.
     * @param methodParameter the method parameter specification
     * @return the corresponding generic parameter type
     * @deprecated as of Spring 4.0, use {@link SimpleParameter#getGenericParameterType()}
     */
    @Deprecated
    public static Type getTargetType(SimpleParameter methodParameter) {
        Preconditions.checkNotNull(methodParameter, "MethodParameter must not be null");
        return methodParameter.getGenericParameterType();
    }

    /**
     * Determine the target type for the given generic parameter type.
     * @param methodParameter the method parameter specification
     * @param implementationClass the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     */
    public static Class<?> resolveParameterType(SimpleParameter methodParameter, Class<?> implementationClass) {
        Preconditions.checkNotNull(methodParameter, "MethodParameter must not be null");
        Preconditions.checkNotNull(implementationClass, "Class must not be null");
        methodParameter.setContainingClass(implementationClass);
        ResolvableType.resolveMethodParameter(methodParameter);
        return methodParameter.getParameterType();
    }

    /**
     * Determine the target type for the generic return type of the given method,
     * where formal type variables are declared on the given class.
     * @param method the method to introspect
     * @param clazz the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     */
    public static Class<?> resolveReturnType(Method method, Class<?> clazz) {
        Preconditions.checkNotNull(method, "Method must not be null");
        Preconditions.checkNotNull(clazz, "Class must not be null");
        return ResolvableType.forMethodReturnType(method, clazz).resolve(method.getReturnType());
    }

    /**
     * Determine the target type for the generic return type of the given
     * <em>generic method</em>, where formal type variables are declared on
     * the given method itself.
     * <p>For example, given a factory method with the following signature,
     * if {@code resolveReturnTypeForGenericMethod()} is invoked with the reflected
     * method for {@code creatProxy()} and an {@code Object[]} array containing
     * {@code MyService.class}, {@code resolveReturnTypeForGenericMethod()} will
     * infer that the target return type is {@code MyService}.
     * <pre class="code">{@code public static <T> T createProxy(Class<T> clazz)}</pre>
     * <h4>Possible Return Values</h4>
     * <ul>
     * <li>the target return type, if it can be inferred</li>
     * <li>the {@linkplain Method#getReturnType() standard return type}, if
     * the given {@code method} does not declare any {@linkplain
     * Method#getTypeParameters() formal type variables}</li>
     * <li>the {@linkplain Method#getReturnType() standard return type}, if the
     * target return type cannot be inferred (e.g., due to type erasure)</li>
     * <li>{@code null}, if the length of the given arguments array is shorter
     * than the length of the {@linkplain
     * Method#getGenericParameterTypes() formal argument list} for the given
     * method</li>
     * </ul>
     * @param method the method to introspect, never {@code null}
     * @param args the arguments that will be supplied to the method when it is
     * invoked (never {@code null})
     * @param classLoader the ClassLoader to resolve class names against, if necessary
     * (may be {@code null})
     * @return the resolved target return type, the standard return type, or {@code null}
     * @since 3.2.5
     * @deprecated as of Spring Framework 4.3.8, superseded by {@link ResolvableType} usage
     */
    @Deprecated
    public static Class<?> resolveReturnTypeForGenericMethod(Method method, Object[] args, ClassLoader classLoader) {
        Preconditions.checkNotNull(method, "Method must not be null");
        Preconditions.checkNotNull(args, "Argument array must not be null");

        TypeVariable<Method>[] declaredTypeVariables = method.getTypeParameters();
        Type genericReturnType = method.getGenericReturnType();
        Type[] methodArgumentTypes = method.getGenericParameterTypes();

        // No declared type variables to inspect, so just return the standard return type.
        if (declaredTypeVariables.length == 0) {
            return method.getReturnType();
        }

        // The supplied argument list is too short for the method's signature, so
        // return null, since such a method invocation would fail.
        if (args.length < methodArgumentTypes.length) {
            return null;
        }

        // Ensure that the type variable (e.g., T) is declared directly on the method
        // itself (e.g., via <T>), not on the enclosing class or interface.
        boolean locallyDeclaredTypeVariableMatchesReturnType = false;
        for (TypeVariable<Method> currentTypeVariable : declaredTypeVariables) {
            if (currentTypeVariable.equals(genericReturnType)) {
                locallyDeclaredTypeVariableMatchesReturnType = true;
                break;
            }
        }

        if (locallyDeclaredTypeVariableMatchesReturnType) {
            for (int i = 0; i < methodArgumentTypes.length; i++) {
                Type currentMethodArgumentType = methodArgumentTypes[i];
                if (currentMethodArgumentType.equals(genericReturnType)) {
                    return args[i].getClass();
                }
                if (currentMethodArgumentType instanceof ParameterizedType) {
                    ParameterizedType parameterizedType = (ParameterizedType) currentMethodArgumentType;
                    Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
                    for (Type typeArg : actualTypeArguments) {
                        if (typeArg.equals(genericReturnType)) {
                            Object arg = args[i];
                            if (arg instanceof Class) {
                                return (Class<?>) arg;
                            }
                            else if (arg instanceof String && classLoader != null) {
                                try {
                                    return classLoader.loadClass((String) arg);
                                }
                                catch (ClassNotFoundException ex) {
                                    throw new IllegalStateException(
                                            "Could not resolve specific class name argument [" + arg + "]", ex);
                                }
                            }
                            else {
                                // Consider adding logic to determine the class of the typeArg, if possible.
                                // For now, just fall back...
                                return method.getReturnType();
                            }
                        }
                    }
                }
            }
        }

        // Fall back...
        return method.getReturnType();
    }

    /**
     * Resolve the single type argument of the given generic interface against the given
     * target method which is assumed to return the given interface or an implementation
     * of it.
     * @param method the target method to check the return type of
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved parameter type of the method return type, or {@code null}
     * if not resolvable or if the single argument is of type {@link WildcardType}.
     */
    public static Class<?> resolveReturnTypeArgument(Method method, Class<?> genericIfc) {
        Preconditions.checkNotNull(method, "Method must not be null");
        ResolvableType resolvableType = ResolvableType.forMethodReturnType(method).as(genericIfc);
        if (!resolvableType.hasGenerics() || resolvableType.getType() instanceof WildcardType) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    /**
     * Resolve the single type argument of the given generic interface against
     * the given target class which is assumed to implement the generic interface
     * and possibly declare a concrete type for its type variable.
     * @param clazz the target class to check against
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved type of the argument, or {@code null} if not resolvable
     */
    public static Class<?> resolveTypeArgument(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType resolvableType = ResolvableType.forClass(clazz).as(genericIfc);
        if (!resolvableType.hasGenerics()) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    private static Class<?> getSingleGeneric(ResolvableType resolvableType) {
        if (resolvableType.getGenerics().length > 1) {
            throw new IllegalArgumentException("Expected 1 type argument on generic interface [" +
                    resolvableType + "] but found " + resolvableType.getGenerics().length);
        }
        return resolvableType.getGeneric().resolve();
    }


    /**
     * Resolve the type arguments of the given generic interface against the given
     * target class which is assumed to implement the generic interface and possibly
     * declare concrete types for its type variables.
     * @param clazz the target class to check against
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved type of each argument, with the array size matching the
     * number of actual type arguments, or {@code null} if not resolvable
     */
    public static Class<?>[] resolveTypeArguments(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType type = ResolvableType.forClass(clazz).as(genericIfc);
        if (!type.hasGenerics() || type.isEntirelyUnresolvable()) {
            return null;
        }
        return type.resolveGenerics(Object.class);
    }

    /**
     * Resolve the specified generic type against the given TypeVariable map.
     * <p>Used by Spring Data.
     * @param genericType the generic type to resolve
     * @param map the TypeVariable Map to resolved against
     * @return the type if it resolves to a Class, or {@code Object.class} otherwise
     */
    @SuppressWarnings("rawtypes")
    public static Class<?> resolveType(Type genericType, Map<TypeVariable, Type> map) {
        return ResolvableType.forType(genericType, new TypeVariableMapVariableResolver(map)).resolve(Object.class);
    }

    /**
     * Build a mapping of {@link TypeVariable#getName TypeVariable names} to
     * {@link Class concrete classes} for the specified {@link Class}.
     * Searches all super types, enclosing types and interfaces.
     * @see #resolveType(Type, Map)
     */
    @SuppressWarnings("rawtypes")
    public static Map<TypeVariable, Type> getTypeVariableMap(Class<?> clazz) {
        Map<TypeVariable, Type> typeVariableMap = typeVariableCache.get(clazz);
        if (typeVariableMap == null) {
            typeVariableMap = new HashMap<TypeVariable, Type>();
            buildTypeVariableMap(ResolvableType.forClass(clazz), typeVariableMap);
            typeVariableCache.put(clazz, Collections.unmodifiableMap(typeVariableMap));
        }
        return typeVariableMap;
    }

    @SuppressWarnings("rawtypes")
    private static void buildTypeVariableMap(ResolvableType type, Map<TypeVariable, Type> typeVariableMap) {
        if (type != ResolvableType.NONE) {
            if (type.getType() instanceof ParameterizedType) {
                TypeVariable<?>[] variables = type.resolve().getTypeParameters();
                for (int i = 0; i < variables.length; i++) {
                    ResolvableType generic = type.getGeneric(i);
                    while (generic.getType() instanceof TypeVariable<?>) {
                        generic = generic.resolveType();
                    }
                    if (generic != ResolvableType.NONE) {
                        typeVariableMap.put(variables[i], generic.getType());
                    }
                }
            }
            buildTypeVariableMap(type.getSuperType(), typeVariableMap);
            for (ResolvableType interfaceType : type.getInterfaces()) {
                buildTypeVariableMap(interfaceType, typeVariableMap);
            }
            if (type.resolve().isMemberClass()) {
                buildTypeVariableMap(ResolvableType.forClass(type.resolve().getEnclosingClass()), typeVariableMap);
            }
        }
    }


    @SuppressWarnings({"serial", "rawtypes"})
    private static class TypeVariableMapVariableResolver implements ResolvableType.VariableResolver {

        private final Map<TypeVariable, Type> typeVariableMap;

        public TypeVariableMapVariableResolver(Map<TypeVariable, Type> typeVariableMap) {
            this.typeVariableMap = typeVariableMap;
        }

        @Override
        public ResolvableType resolveVariable(TypeVariable<?> variable) {
            Type type = this.typeVariableMap.get(variable);
            return (type != null ? ResolvableType.forType(type) : null);
        }

        @Override
        public Object getSource() {
            return this.typeVariableMap;
        }
    }

    private GenericTypeResolver(){

    }
}